1. The Field of the Invention
The present invention relates generally to vehicular traffic monitoring systems, and more particularly relates to sensors for detecting the presence, location, speed, direction of travel, volume, and occupancy of vehicular traffic on a roadway.
2. The Relevant Technology
Controlled signalized intersections represent a key element in urban planning, public safety and traffic control. The science and engineering of traffic planning and control has long relied on the use of sensor devices designed for this specific purpose and, more recently, for the collection of traffic flow data. Some of these device technologies, such as those embedded in the roadways, have been employed for over sixty years and continue to require the same amount of attention in installation, calibration, maintenance, repair and replacement as they did decades ago. This laborious caretaking can be due to a number of factors ranging from inferior product design and poor installation to post installation disruption and migratory changes in traffic flow patterns. Reliability of these technologies is an issue to an overall traffic control plan and can prove extremely costly to maintain as an integral component to an overall traffic plan.
Traffic control devices that are embedded in roadways serve the interest of public safety, but in the event of a new installation, or maintenance/repair, they act as a public nuisance, as repair crews are required to constrict or close multiple lanes of traffic for several hours to reconfigure a device, or even worse, dig up the failed devices for replacement causing closure of the lane for several days or weeks.
While several sensor technologies are employed to assist in traffic planning and control, the oldest and most widely used technology currently employed in controlled intersections is the inductive loop. This loop is an in-pavement fixed location sensor, with the limitation of sensing only the traffic that is immediately over it. While such devices have continued history of use, failures of loops are common and at any one time as many as 20%–30% of all installed controlled intersection loops are non-responsive. Furthermore, the cost to repair these devices can be greater than the original installation cost.
As technology has developed over the decades, new sensory devices have been introduced to the traffic control industry. In recent years, there have emerged several non-intrusive technologies for traffic sensing that employ a remote sensor (i.e., not embedded in the roadway) as illustrated in FIG. 1. While the majority of these types of sensors 110 incorporate microwave radar technology, other types including optical devices have also taken hold. For example, intersection traffic cameras may be manually configured to analyze specific user-defined traffic zones at all times. As cameras rely on optics, (i.e., the ability to visually see the traffic that is to be monitored) they are susceptible to the forces of nature that can occlude visibility. These forces include sun glare, accumulated snow or dirt and darkness. Under ideal conditions cameras would only need to be serviced or reconfigured with major intersection redesign. Presently available systems require on-site attention to improve and upgrade the capability of the unit, or complete replacement for upgrading the camera itself.
Another type of above-ground sensor includes acoustic sensors which operate as traffic sound-based listening devices. These devices employ an array of microphones built into the sensor allowing the device to detect traffic based on spatial processing changes in sound waves received at the sensor. After processing and analysis of the received sound waves, detection and traffic flow information is then assigned to the appropriate user-defined regions or lane being monitored forming a picture of the traffic.
When acoustic sensors are deployed, their microphone sensitivity is pre-set for normal operating conditions which include typical weather conditions. Again, the software and operating instructions to control an acoustic sensor require on-site attention to improve and upgrade the capability of the unit, or complete replacement to upgrade the sensor itself.
Other popular sensor types are based on microwave radar technology. Such sensors detect traffic based on the reflection of a transmitted electromagnetic signal depicted in FIG. 1 as signals 118. The received signal is then processed into detection and traffic flow information which is then assigned to the appropriate user defined lane being monitored. As illustrated in FIGS. 2 and 3, microwave radar technology utilizes several bulky, expensive and manufacturably inefficient components to sense traffic. Most notably, microwave radar sensors are comprised of a mechanically-large horn antenna 170 and separate radio frequency components and controller boards that are individually tuned and matched in order to result in an operable system 180. Furthermore, the unit requires on-site maintenance and attention to reconfigure, or upgrade software.
As identified above, many useful forms of technology exist to monitor and detect traffic. However, many forms of detection are obtrusively bulky, manufacturing intense, and all require on site maintenance and attention to re-configure the software, or operating instructions when traffic conditions, climate, or other operating conditions change. Without reconfiguration, the devices will continue to sense, but with reduced accuracy and in the worst case they may discard the actual flow pattern as peripheral noise. The cost to manufacture and reconfigure devices can be costly, and disruption to traffic is common.